I'm trying to connect to both a single node Redis and Elasticache cluster with the same code base. I am using Jedis raw not via Spring since this is a legacy app and I am setting up Tomcat to use Jedis as a session store.
Does Jedis need to know all the cluster IPs to function or can it work with just one and let it figure out the others automatically?
It can work with just one active node and then figuring out the other nodes internally.
Related
I would like to be able to query the h2 in memory database for each Corda node concurrently, but am unable to do so currently. Does anybody have a workaround?
Like Alessandro described, you're going to want to follow this guide (https://docs.corda.net/docs/corda-os/4.7/node-database-access-h2.html) to connect to your nodes.
It shouldn't make a difference how many connections you make to it or which nodes. The H2 db should work like you expect.
If there are multiple read replicas, where load balancing related settings can be specified when using spring AWS libraries.
Read replicas have their own endpoint address similar to the original RDS instance. Your application will need to take care of using all the replicas and to switch between them. You'd need to introduce this algorithm into your application so it automatically detects which RDS instance it should connect to in turn. The following links can help:
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Overview.Replication.html#Overview.ReadReplica
We have a memcached cluster running in production as a cache layer on top of MySQL. Now we are considering to replace memcached with Couchbase to avoid the cold cache issue (in case of crash) and have this nice feature of managed cache cluster.
At the same time, we want to minimize the changes to migrate to Couchbase. One way we can try is to maintain the libmemcached API and set up a http proxy to direct all request to Couchbase. This way nothing is changed in the application code. If I understand correctly, this way Couchbase is basically a managed memcache cluster. We didn't take advantage of the persistence cache items. We can't do something like flagging a certain cached item to be persistent:
# connect to couchbase like connecting to memcached
$ telnet localhost 11211
SET foo "foo value" # How can we make this item persistent in Couchbase?
I assume this is because all items are stored in memcached bucket. So the question becomes:
Can we control which item to be stored in Couchbase bucket or
memcache bucket? To do so, do we have to change libmemcached API and all the application code related to that?
Thanks!
I think you should look into running Moxi, which is a memcached proxy to couchbase. You can configure Moxi with the destination couchbase bucket.
A couchbase cluster automatically spins up a cluster-aware moxi gateway, which you could point your web/application servers to. This is what couchbase calls "server-side moxi".
Alternatively, you can either install moxi on each your web/app servers, so they simply connect to localhost:11211. Moxi handles the persistent connection the couchbase cluster. This is what couchbase calls "client-side moxi".
SnappyData documentation and architecture diagrams seem to indicate that a JDBC thin client connection goes from a client to a Locator and then it is routed to a direct connection to a Server.
If this is true, then I can run JDBC queries without a Lead node, correct?
Yes, that is correct. The locator provides load and connectivity information back to the client that is now able to connect to one or more servers either for direct access to a bucket for low latency queries but more importantly, is HA - can failover and failback.
So, yes, your connected clients will continue to function even when the locator goes away. Note that the "lead" plays a different role than the locator. Its primary function is to host Spark driver, orchestrate Spark Jobs and provide HA to Spark. With no lead, you won't be able to run such Jobs.
In addition to what #jagsr has mentioned, if you do not intend to run the lead nodes (and thus no Spark jobs or column store), then you can run the cluster as pure row store using snappy-start-all.sh rowstore (see rowstore docs)
I'm deploying my Grails (2.3.6) app with the Grails Standalone App Runner plugin, like so:
grails -Dgrails.env=prod build-standalone myapp.jar --tomcat
Then, my CI build places myapp.jar onto my app server, say, myapp01.
I now want to cluster app sessions when myapp is running on multiple nodes. So if myapp gets deployed to myapp01, myapp02 and myapp03, and one of those instances starts a new session with a user, I want all 3 to be aware of the same session. This is obviously so I can put all the nodes behind a load balanced URL (http://myapp.example.com, etc.) and it doesn't matter what node you get routed to: all nodes share the same sessions.
I googled "grails session clustering" and see a bunch of articles that seem to require terracotta, but I also heard that Grails has built-in session clustering facilities. But any searches I do come back empty-handed.
So I ask: How can I achieve this kind of session clustering with an embedded Tomcat?
Besides the seesion-cookie plugin that #injecteer proposed, there are several other plugins allowing to keep sessions in a shared storage (DB, mongodb, redis, memcached) that can be accessed by any of your tomcat instances. Take a look at these:
http://grails.org/plugin/database-session
http://grails.org/plugin/mongodb-session
http://grails.org/plugin/redis-database-session
http://grails.org/plugin/standalone-tomcat-redis
http://grails.org/plugin/standalone-tomcat-memcached
I never heard of something like this out-of-box. I would give 2 options a try:
Use a session-cookie plugin, with which you decouple your clients from storing the sessions in tomcat
Use or implement persistent sessions, which are stored in some sort of DB and are not bound to any tomcat instance.
You could achieve this by using the tomcat build-in functionality. Tomcat instance node could replicate session from others, then all the session get shared between nodes.
You can do this in at least three ways:
Session Replication by using Muilcast between instance nodes.
Session Replication just between primary and secondary node backup.
Session Replication between Static Memberships, this one is useful when the multicast cannot be enabled or supported such as in AWS EC2 Env.
Reference:
http://tomcat.apache.org/tomcat-7.0-doc/cluster-howto.html
http://khaidoan.wikidot.com/tomcat-cluster-session-replication